﻿HYDROLOGY 
  OP 
  NEW 
  YORK 
  379 
  

  

  l)y 
  10 
  feet 
  6 
  inches 
  (or 
  4 
  per 
  cent) 
  for 
  all 
  depths 
  less 
  than 
  8 
  

   inches, 
  while 
  the 
  length 
  between 
  wingwalls 
  heretofore 
  used 
  was 
  

   substantially 
  correct. 
  It 
  was 
  also 
  found 
  that 
  the 
  dam 
  crest 
  is 
  

   not 
  absolutely 
  level 
  because 
  of 
  settlement 
  near 
  the 
  center 
  pier, 
  

   and 
  that 
  the 
  method 
  of 
  measuring 
  the 
  depth 
  gave 
  results 
  about 
  

   O.30 
  inch 
  too 
  high. 
  

  

  2) 
  The 
  how 
  in 
  the 
  old 
  Croton 
  aqueduct 
  at 
  the 
  depth 
  commonly 
  

   used 
  before 
  the 
  new 
  aqueduct 
  was 
  opened 
  is 
  less 
  than 
  previously 
  

   estimated 
  by 
  about 
  14,000,000 
  gallons 
  per 
  day, 
  or 
  15 
  per 
  cent. 
  

   These 
  earlier 
  estimates 
  were 
  based 
  on 
  using 
  for 
  the 
  old 
  Croton 
  

   aqueduct 
  the 
  same 
  coefficient 
  of 
  flow 
  found 
  for 
  the 
  new, 
  smooth 
  

   and 
  clean 
  Sudbury 
  aqueduct, 
  and 
  not 
  upon 
  a 
  gaging 
  of 
  the 
  old 
  

   aqueduct 
  itself. 
  

  

  3) 
  Gaged 
  by 
  the 
  same 
  observer 
  with 
  the 
  same 
  instrument, 
  the 
  

   new 
  Croton 
  aqueduct 
  is 
  now 
  delivering 
  less 
  water 
  for 
  a 
  given 
  

   depth 
  of 
  flow 
  than 
  when 
  new, 
  to 
  the 
  extent 
  of 
  about 
  40,000,000 
  

   gallons 
  per 
  day; 
  or, 
  when 
  the 
  depth 
  measured 
  at 
  the 
  head 
  of 
  the 
  

   aqueduct 
  is 
  11 
  feet, 
  the 
  shortage 
  is 
  about 
  15 
  per 
  cent. 
  

  

  4) 
  An 
  error 
  was 
  made 
  five 
  years 
  ago 
  in 
  setting 
  the 
  gage 
  by 
  

   which 
  depths 
  in 
  the 
  new 
  aqueduct 
  are 
  read, 
  so 
  that 
  it 
  makes 
  the 
  

   depth 
  appear 
  2J 
  inches 
  too 
  large; 
  this 
  cause 
  alone 
  contributes 
  

   about 
  6,000,000 
  gallons 
  per 
  day 
  to 
  the 
  overestimate 
  mentioned 
  

   above. 
  

  

  5) 
  The 
  effect 
  of 
  storage 
  drawn 
  from 
  Boyd's 
  Corner 
  and 
  Middle 
  

   Branch 
  reservoirs 
  and 
  the 
  Croton 
  lake 
  in 
  modifying 
  the 
  natural 
  

   flow 
  had 
  not 
  been 
  taken 
  into 
  account 
  in 
  these 
  earlier 
  estimates, 
  

   neither 
  had 
  due 
  allowance 
  been 
  made 
  for 
  the 
  controlled 
  natural 
  

   ponds. 
  1 
  

  

  Croton 
  river 
  is 
  an 
  average 
  water 
  yielder. 
  The 
  minimum 
  yield 
  

   for 
  a 
  complete 
  water 
  year 
  for 
  the 
  whole 
  period 
  1868-1899, 
  in- 
  

   clusive, 
  was 
  in 
  1880, 
  when 
  from 
  December 
  to 
  November, 
  inclusive, 
  

   the 
  total 
  runoff 
  was 
  13.71 
  inches. 
  

  

  The 
  Croton 
  catchment 
  contains 
  thirty-one 
  lakes 
  and 
  ponds, 
  

   many 
  of 
  which 
  have 
  been 
  utilized 
  as 
  natural 
  storage 
  basins 
  by 
  

   constructing 
  dams 
  at 
  their 
  outlets. 
  The 
  following 
  tabulation 
  

   gives 
  the 
  entire 
  natural 
  and 
  artificial 
  storage, 
  either 
  actually 
  

   carried 
  out 
  or 
  under 
  construction 
  in 
  1902, 
  for 
  the 
  Croton 
  catch- 
  

   ment 
  area: 
  

  

  l 
  Freeman's 
  report, 
  pp. 
  121-123. 
  

  

  